Widespread use of asphalt based road pavements in place of concrete has lead to search for additives to prevent rutting and cracking of road surface over long term. Commonly used additive at present is Styrene Butadiene Styrene block copolymer (SBS). The high cost of SBS has resulted in many alternative products. Many of these alternative products are polymer based-some recycled rubbers mostly from used tire rubber in powder form for ease of dispersion.
Many other polymers have traditionally been used for improving the performance of asphalt. Among them are Natural Rubber (polyisoprene) and Butyl Rubber (Isobutylene-isoprene copolymer). These additives in small doses ranging from 3 to 10% in the asphalt improve resistance to rutting and cracking of asphalt bound aggregate pavements. Also it increases the softening point and viscosity of asphalt. With increasing cost of Natural and Butyl Rubbers, the addition of these rubbers in virgin form has escalated the cost of such treatment. The authors of this patent with background in development of devulcanized polymers have come up with a novel solution for use of post consumer Butyl rubber scraps and pre-consumer, post manufacturing waste polyisoprene as asphalt additive that would replace partly or fully virgin Butyl and polyiosprene rubbers. This not only makes more economical sense, but also meets the federal mandate to increase scrap rubber content in asphalt, thereby prevent these scraps from landfills.
Natural Rubber and synthetic Polyiosprene are used in many rubber products ranging from tires to rubber threads. Their post consumer wastes are mostly sent to landfills. In case of used tires, most of it is used in furnaces for boilers and kilns. Although they are burnt, the process produces emissions that are detrimental to the environment. Therefore their use in asphalt would be environment friendly.
Butyl Rubber bladders are extensively used in the manufacturing process of making tires. For every 100 tires a bladder weighing anywhere between 20 LB and 50 LB is discarded. They go to landfills at present. These can be used in the present invention as a component to produce asphalt additive.
A number of patents exist that use polymer additives to improve certain characteristics of asphalts. U.S. Pat. No. 6,214,908 uses a blend of polypropylene plastic resin, Styrene Butadiene Rubber and Calcium Carbonate mineral filler as an additive for asphalt. U.S. Pat. No. 5,801,204 describes use of liquid plastic as asphalt additive while U.S. Pat. No. 5,702,199 discloses the use granulated recycled plastic waste to replace or substitute some of the rock aggregate as component of asphalt additive for use in pavement.
None of above referenced patents discloses the use of post consumer butyl rubber, pre consumer polyiosprene and plastics resin blends as asphalt additives.